1. Field of the Invention
The present invention relates to a method and apparatus for transmitting messages in a radio network environment, and more particularly, to a method and apparatus for effectively transmitting messages in a radio network environment according to a mobile internet protocol (MIP).
2. Description of the Related Art
As the performances of mobile nodes, such as notebook computers and personal digital assistants (PDAs) have been improved and mobile communication technologies have been developed, the number of mobile node users has significantly increased. Accordingly, a mobile internet protocol (MIP) that uses an internet protocol (IP) address as a mobile node identifier has been introduced. In particular, MIP is a technology whereby even if the location of a mobile node is changed, a node can continuously communicate with a mobile node by using the IP address of the mobile node.
FIG. 1 is a diagram of a related art wireless network environment. Referring to FIG. 1, the related art wireless network environment includes a home agent (HA) 11, an access point (AP) A 12, a mobile node (MN) 13, a correspondent node (CN) 14, a foreign agent (FA) A 15, an AP B 16, a FA B 17, and an AP C 18.
Each of the HA 11, the FA A 15, and the FA B 17, which are a type of access router (AR), manages a subnet in which it is located. That is, the HA 11 manages a subnet A, the FA A 15 manages a subnet C, and the FA B 17 manages a subnet D. The AP A 12, the AP B 16, and the AP C 18 communicate with ARs, such as the HA 11, the FA A 15, and the FA B 17, by wire, and communicate with the MN 13 wirelessly to connect the MN 13 to a wired network.
When the CN 14 transmits a packet using the IP address of the MN 13 as a destination address, the packet is processed according to the MIP, as follows. If the MN 13 is located in the subnet A managed by the HA 11, the packet arrives at the MN 13 via the HA 11 and the AP A 12. However, if the MN 13 leaves the subnet A and is then located in the subnet C managed by the FA A 15, the HA 11 intercepts the packet and delivers it to the FA A 15 by tunneling. In this case, the current IP address of the MN 13, which is referred to as a COA (Care Of Address), becomes different from the original IP address thereof. In order to perform tunneling, the HA 11 must recognize the COA of the MN 13. Thus, the MN 13 transmits a binding update message containing information, such as the COA of the MN 13, to the HA 11. Similarly, the packet is processed as described above when the MN 13 leaves the subnet C and is moved to the subnet D managed by the FA A 17.
FIG. 2 is a diagram illustrating a handover process in a related art wireless network environment. Referring to FIG. 2, an MN 25 sequentially passes through a cell managed by an AP A 22, a cell managed by an AP B 23, and a cell managed by an AP C 24. The MN 25 must generate a COA for use in a subnet in which it is now located in order that the MN 25 can communicate with other nodes while moving in a subnet managed by an AR 21, the COA containing a subnet prefix. Thus, the MN 25 must have information regarding the subnet to generate the COA.
Thus, the AR 21 periodically broadcasts a router advertisement (RA) message containing the information regarding the subnet. Also, the MN 25 may transmit a router solicitation (RS) message requesting transmission of the RA message. However, the RA message that is periodically broadcast is rebroadcast to the MN 13 by the AP A 22, the AP B 23, or the AP C 24 that wirelessly receive the RA message from the AR 21. In this case, unlike wired resources, wireless resource bandwidth for a wireless channel is significantly limited, and thus, broadcasting of the RA message causes serious waste of wireless channel bandwidth.
In particular, if a large amount of time is needed to perform a handover process in which the MN 25 moves from a subnet managed by the AR 21 to a new subnet, communications established with the MN 25 is discontinued, thereby degrading the communication performance of the MN 25. Thus, the handover process must be expedited. However, when a transmission interval during which the RA message is transmitted is shortened to expedite the handover process, waste of wireless channel bandwidth becomes worse. Also, when the MN 25 transmits the RS message and the RA message is broadcast in response to the RS message, waste of wireless channel bandwidth is substantial.